As of this writing (December 2010), three of the four nationwide cellular carriers offer some form of 4G wireless service.
Sprint's 4G network uses WiMax technology, which Sprint says can deliver average download speeds between 3 mbps and 6 mbps, with bursts up to 10 mbps. The network can deliver upload speeds of up to 1 mbps.
To see if you have access to Sprint's service, see Where is Sprint's 4G Network Available?.
Verizon Wireless, meanwhile, uses a technology called Long Term Evolution, or LTE. Verizon's LTE network can deliver download speeds between 5 mbps and 12 mbps. Verizon also says it will offer upload speeds between 2 mbps and 5 mbps.
To see if you have access to Verizon's service, see Where is Verizon's 4G Network Available?.
T-Mobile's HSPA+ network is not a true 4G network, but does deliver speeds faster than a typical 3G network; it's considered more of a 3.5G network than a true 4G network. T-Mobile says it can offer download speeds between 5 mbps and 8 mbps.
To see if you have access to T-Mobile's service, see Where is T-Mobiles HSPA+ Network Available?.
AT&T does not yet offer 4G service, but plans to do so starting next year.